Modern electronic control modules products are typically constructed using circuit components mounted to a substrate, often a printed circuit board. Some of these control modules are constructed using molded printed circuit boards. Molded printed circuit boards can be fabricated using what is commonly referred to as two-color plastic. In this type of structure the two plastics are sequentially molded into an appropriate shape to hold the circuit components. One of the two plastic materials can be plated with metal that, once soldered, acts to physically captivate and electrically connect the circuit components.
An attribute of the two-color plastic process is that it can be used to construct housings for enclosing the substrate described above. In fact, the substrate and the housing can be fabricated as one physical part, rather than two separate components. This type of structure is often referred to as a Molded Interconnect Device (MID).
An important performance requirement of control modules is to deliver significant amounts of energy. While delivering this energy heat is generated by certain of those circuit components, typically power transistors, as a byproduct of the inefficiency of those circuit components. Heat can significantly shorten the life of all of the circuit components of the control module and so a mechanism for conducting the heat away from those circuit components is required. Plastic is not an efficient conductor of heat.
Conventional approaches for conducting heat include heat-sink structures that are tightly thermally-coupled to the power transistors (and other heat generating components). These heat-sinks are positioned physically to isolate the generated heat from the non-heat-generating circuit components, and also to efficiently remove heat from the heat-generating components. Typically, heat-sinks are constructed of a metal material.
Manufacturing electronic control modules with metal heat-sinks is bothersome. For one, a separate component needs to be assembled to the control module. Managing the manufacture of the metal heat-sink, and guarantying an efficient thermal coupling during the life of the control module between the heat-generating circuit components and the metal heat-sink, is difficult at best.
Moreover, metal heat-sinks add undesirable mass to the control module, which in adverse vibration and shock environments such as in an automotive application, can significantly shorten the useful life of the control module because of physical failure of the coupling between the heat-generating circuit components and the metal heat-sink.
Additionally, for metal heat-sinks to be thermally efficient they are typically mounted between the heat-generating circuit components and an outside surface of the control module. This arrangement is difficult to seal against external contaminants--such as those found in an automotive environment.
Electrical isolation between various heat-generating circuit components is also important in many applications. Conventionally, either separate heat-sinks, or electrical isolation devices are use to effect this electrical isolation. Electrical isolation devices add to the thermal inefficiency of the structure.
What is needed is a simple, minimum component, with thermally efficient electrical isolation, and which offers an environmentally robust and reliable heat-sinking solution for control module packaging.